To export data from a .PST file, you must run the Export-Mailbox cmdlet on a 32-bit computer that has the 32-bit version of the Exchange management tools and Outlook 2003 Service Pack 2 (SP2) or Outlook 2007 installed.

Please be aware that there are prerequisites to exporting mailboxes. You need a location to export the mailbox to along with permissions set on the mailbox.